F5

[TSRobot]

Hi. For my F5 130 pds i have 24mm 1.25inch 68 degree maxvision which gives me lovely wide sharp views nearly to the edge. I've tried an SWA 32mm 70 degree, but this showed so much blur with only a bit sharp in the middle 50% or so.

What would folk recommend thats wider than my 24 mv but can give equal quality views? 28,30?

Thank you. I made a mistake with my SWA  32mm 70 degree and now i just feel like binning it :$ 

[SnakeyJ]

At F5 it might be worth looking at a coma corrector to correct theses wider field views!    I got a Celestron Ultima LX that gave very decent views with my old F5 AR152/760 nr petzval, but in my SW 200P it was always paired with the coma corrector.

[TSRobot]

I've no idea how the SW or baader CC fits and then how eyepieces fit on top of that. Any pictures would be welcome as I can't find any on the net. Thanks Snakeyj for your reply.

[Ruud]

You have a Newtonian. I understand that for parabolic mirrors coma increases approximately proportionally to the distance from the optical axis. So in Newtonians, everything else being equal, longer focal length eyepieces, having wider field stops, pick up more coma at the outer edge, but... the magnification decreases by the same factor, which means that the observed amount of coma should stay the same.

Although it is not generated by the eyepiece, the coma you'll see does increase with the apparent field of view of the eyepiece. If the view at 68° is fine to you, you may not need a coma corrector unless you move to UWA or beyond.

The 68° of the 24mm Maxvision and 70° of your 32mm SWA are much alike, so it is possible that your 32mm 70° eyepiece performed poorly for other reasons.

One likely reason would be that the 32mm 70° is is not well corrected for fast telescopes. Not all eyepieces perform well off axis at f/5.

Another reason could be a poor match of objective and eyepiece field curvatures. Field curvature increases non-linearly with the distance to the optical axis. Ideally the focal planes of the objective and the eyepiece should both be flat like so: ||. You can also get a good fit when the curvature of the focal planes match like this: )) or this: ((. Less fortunate combinations of focal planes are |(, |), )| and (|, and you get really poor performance when the focal planes of objective and eyepiece do not match at all, like )( and (). Your eyes may not have sufficient dioptre accommodation for a bad combination of objective and eyepiece, and the field curvature of your particular 32mm 70° may be a bad match to your Newtonian.

Fortunately, the Maxvisions handle f/5 pretty well and their fields seem mostly flat. Problems with field curvature, though, only become apparent when the observer's eye has a limited range of dioptre adjustment, so I can't say whether a 28mm or 34mm Maxvision 68° will work as well for you as for me. The coma you see in either of those should at least be equal  to what you see in your 24mm.

The Meade 4K SWA, ES 68° and TV Panoptic have similar performance to the Maxvision 68°.

[Damo636]

Without knowing your budget, I'll go ahead and recommend the 30mm Explore Scientific 82° ( I'm assuming the 130pds accepts 2"?)......

https://www.firstlightoptics.com/explore-scientific-eyepieces/explore-scientific-82-degree-series-eyepieces.html

 

I've used this with my 12" f5 and thought it excellent. 

[TSRobot]

Maybe the coma corrector is the way to go. Trouble is that just like buying a washing machine or kettle, there is no way of trying this before good money goes in the bin. The SW CC reduces the F ration further and so increases exit pupil. Then my SW SWA 32mm 70 degree might become better corrected, but with a 7mm + exit pupil. No win for either way for the SW SWA 32mm 70 degree ep. It's a good door stop BTW.

Edit. Have just found this useful picture at Altair astro of the SW CC assembly. They also have it quite cheep. £99

[Ricochet]

18 hours ago, TSRobot said:

Hi. For my F5 130 pds i have 24mm 1.25inch 68 degree maxvision which gives me lovely wide sharp views nearly to the edge. I've tried an SWA 32mm 70 degree, but this showed so much blur with only a bit sharp in the middle 50% or so.

What would folk recommend thats wider than my 24 mv but can give equal quality views? 28,30?

Thank you. I made a mistake with my SWA  32mm 70 degree and now i just feel like binning it :$ 

I essentially had both of these eyepieces and replaced the pair with a 28mm Nirvana. You're not going to improve the 32mm SWA through a coma corrector because all eyepiece aberrations/distortions will still be there. The only option of equal quality to the 24mm Maxvision  that you could replace the 32mm SWA with is the 34mm ES68/Maxvision/Meade SWA. 

[TSRobot]

38 minutes ago, Ricochet said:

I essentially had both of these eyepieces and replaced the pair with a 28mm Nirvana. You're not going to improve the 32mm SWA through a coma corrector because all eyepiece aberrations/distortions will still be there. The only option of equal quality to the 24mm Maxvision  that you could replace the 32mm SWA with is the 34mm ES68/Maxvision/Meade SWA. 

Thank you. I was trying to find out if the problem with the sw swa 32mm 70degree was inherent with it's optics being better suited to longer slower FR. So no need for a coma corrector to try to correct something that can be corrected to a degree with an alternate eyepiece. A coma corrector will help with coma, but that's all. Eyepiece shopping commences. Thanks everyone 

[John]

1 hour ago, TSRobot said:

Thank you. I was trying to find out if the problem with the sw swa 32mm 70degree was inherent with it's optics being better suited to longer slower FR. So no need for a coma corrector to try to correct something that can be corrected to a degree with an alternate eyepiece. A coma corrector will help with coma, but that's all. Eyepiece shopping commences. Thanks everyone 

I think the only problem with the SW SWA 70's is that they are made to a budget. F/5 is a challenging focal ratio for wide angle eyepieces and many that work well at F/8, F/10 etc will show astigmatism at F/5. The ones that remain astigmatism free right across the field of view at F/5 cost more to design and manufacture and, needless to say, to purchase.

A coma corrector will reduce the coma that the scope optics produce but the astigmatism derived from the eyepiece optics will remain.

 

 

[triton1]

The 32 ultima lx and the 32 sw swa are apparently the worst of the bunch I believe there the same but wearing different clothes.The Maxvision 28 however is excellent it’s probably my most used eyepiece.

[TSRobot]

I've been thinking a lot about the MV 28mm and also the SW Aero 30mm. Both say they are 6 element and the Aero 30mm would give me a bit more FOV and exit pupil of 6mm. The Aero 30mm I think now is discontinued though still showing as in stock at some shops. I've read Johns review of the Aero that seems quite good. Still thinking.......

[John]

The Aero ED 30mm is a good eyepiece but still won't be corrected across the whole field in an F/5 scope I fear. The Maxvsion 68's are better in this respect (still not 100% though) as are the Explore Scientific 68 degree series. F/5 results in a steep light cone which creates real challenges in terms of correction for eyepieces.

 

[TSRobot]

If only we could rent them to try for a bit.......

[John]

8 minutes ago, TSRobot said:

If only we could rent them to try for a bit.......

I was very lucky that First Light Optics were prepared to loan me quite a few over the years to try out and report back on

Eyepiece choice is quite a personal thing. I find the used market helps because you can buy something and re-sell at little or no loss if it does not suit you.

 

[TSRobot]

56 minutes ago, John said:

I was very lucky that First Light Optics were prepared to loan me quite a few over the years to try out and report back on 

Eyepiece choice is quite a personal thing. I find the used market helps because you can buy something and re-sell at little or no loss if it does not suit you.

 

I buy and sell quite often from Astrobuysell, but some of the most loved kit never comes up for sale. I managed to sell my C8 for exactly what I paid for it. The best thing about buying new is that you can return it if it's not quite what you expected and under EU law you get a 2 year warranty, not the 1 year that many claim. Now though buying 2nd hand lets you down when you can't return something that's not compatible. Swings and roundabouts. Never had any trouble with Astrobuysell like the nightmares I've had selling on eBay. 

Maybe if I bought the ES 68s or 82s then I'd never sell because they'd look so good on my mantel piece in my old age?

[rwilkey]

On 28/10/2017 at 01:18, Damo636 said:

Without knowing your budget, I'll go ahead and recommend the 30mm Explore Scientific 82° ( I'm assuming the 130pds accepts 2"?)......

https://www.firstlightoptics.com/explore-scientific-eyepieces/explore-scientific-82-degree-series-eyepieces.html

 

I've used this with my 12" f5 and thought it excellent. 

To be honest, a very good ep, but I think it will be too heavy for the PDS130, also difficult to use for the same reasons as the SW32 70*.  In my opinion the TV 24mm Panoptic would probably offer the best wideview you can get, but a little expensive. 

[TSRobot]

Hi. I've gone for another maxvsion 28mm. The 24mm and 16mm work very well that i already have. The 28mm was reduced by £20 at FLO and should arrive tomorrow. Fingers crossed